Method for digital wireless communications

ABSTRACT

In a multivalue modulation type with one pilot symbol inserted for every 3 or more symbols, signal points of each one symbol immediately before and after a pilot symbol are modulated using a modulation type different from that for pilot symbols. In this way, it is possible to suppress deterioration of the accuracy in estimating the reference phase and amount of frequency offset by pilot symbols and improve the bit error rate characteristic in the signal to noise ratio in quasi-coherent detection with symbols whose symbol synchronization is not completely established.

This application is a continuation application of co-pending U.S.application Ser. No. 11/831,383, filed Jul. 31, 2007, which is adivisional application of U.S. application Ser. No. 10/781,839 (now U.S.Pat. No. 7,359,454), filed on Feb. 20, 2004, which is a Continuation ofU.S. application Ser. No. 10/427,992 (now U.S. Pat. No. 6,748,023),filed May 2, 2003, which is a continuation of U.S. application Ser. No.09/482,892 (now U.S. Pat. No. 6,608,868), filed Jan. 14, 2000, thecontents of which are expressly incorporated by reference herein intheir entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for digital wirelesscommunications using a multivalue modulation type.

2. Description of the Related Art

In a conventional digital mobile wireless communication system, afamiliar example of frame configuration method to estimate a frequencyoffset is described in “Terrestrial Mobile Communication 16QAM FadingDistortion Compensation Method” (Sanbe, TECHNICAL REPORT OF IEICE, B-II,Vol. J-72-B-II, No. 1, pp. 7-15, January 1989). FIG. 1 shows a frameconfiguration according to a 16QAM system.

As shown in FIG. 1, this frame configuration has one pilot symbolinserted for every N−1 information symbols. With such a frameconfiguration, quasi-coherent detection is performed by estimating thereference phase, amount of frequency offset and amount of amplitudedistortion using pilot symbols.

However, during quasi-coherent detection with such a frame configurationwith one pilot symbol inserted for every few information symbols, symbolsynchronization gets the jitters. Therefore, in quasi-coherent detectionwith symbols whose symbol synchronization is not completely established,the accuracy in estimating the reference phase, amount of frequencyoffset and amount of amplitude distortion using pilot symbolsdeteriorates. This results in deterioration of a bit error ratecharacteristic in the signal to noise ratio.

This is explained more specifically using FIG. 2A and FIG. 2B. FIG. 2Aand FIG. 2B are diagrams to explain the relationship between the timeand amplitude of a reception signal. In FIG. 2, reference code 1indicates the time when pilot symbol 3 is detected with an idealjudgment time and reference code 2 indicates the time when pilot symbol3 is detected with a time offset (jitter) generated. Reference code 4indicates the information symbols immediately before and after pilotsymbol 3.

Both a transmitter and receiver are provided with their respective clockgeneration functions. Because of this, the receiver has different clockgeneration sources, and therefore the receiver may detect waves attiming such as time 2, at which a time offset from ideal judgment time 1has occurred. At this time, as shown in FIG. 2A and FIG. 2B, the timeoffset originates errors (amplitude errors) X_(I) and X_(Q) from thesignal point. This deteriorates the error rate. Furthermore, thereceiver estimates the phase, amplitude variation and frequency offseton the I-Q plane from the pilot symbol. However, when detected at time 2when the time offset occurred, the pilot symbol signal has an error fromthe pilot symbol signal point, and therefore the accuracy in estimatingthe phase, amplitude variation and frequency offset deteriorates.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide an apparatus andmethod for digital wireless communications capable of improving theaccuracy in estimating the reference phase and amount of frequencyoffset when the receiver (demodulation side) carries out quasi-coherentdetection and improving the bit error rate characteristic in the signalto noise ratio.

This objective is achieved by a digital wireless communication apparatusthat uses a modulation type including QPSK modulation and modulates thesignal points of each one symbol immediately before and after a pilotsymbol using a modulation type different from the modulation type forthe pilot symbol in a frame configuration with one pilot symbol insertedfor every 3 or more symbols.

This makes it possible to suppress deterioration of the accuracy inestimating the reference phase and amount of frequency offset usingpilot symbols in quasi-coherent detection with symbols whose symbolsynchronization is not completely established and improve the bit errorrate characteristic in the signal to noise ratio.

Furthermore, this objective is also achieved by a digital wirelesscommunication apparatus that increases the amplitude at pilot symbolsignal points more than the maximum amplitude at signal points accordingto the multivalue modulation type with 8 or more values.

This apparatus can not only suppress deterioration in the accuracy inestimating the reference phase, amount of frequency offset by a pilotsymbol in quasi-coherent detection with symbols whose symbolsynchronization is not completely established, but also improve the biterror rate characteristic in the signal to noise ratio withoutdeteriorating the power efficiency of the power amplifier on thetransmitting side.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the invention will appearmore fully hereinafter from a consideration of the following descriptiontaken in connection with the accompanying drawing wherein one example isillustrated by way of example, in which;

FIG. 1 is a diagram showing a frame configuration example of aconventional digital wireless communication apparatus;

FIG. 2A is a diagram showing a relationship between the amplitude andtime when a reception signal (I component) is received;

FIG. 2B is a diagram showing a relationship between the amplitude andtime when a reception signal (Q component) is received;

FIG. 3 is a diagram showing another frame configuration example of theconventional digital wireless communication apparatus;

FIG. 4 is a diagram showing a configuration of the transmitter side of adigital wireless communication apparatus of the present invention;

FIG. 5 is a diagram showing a configuration of the receiver side of thedigital wireless communication apparatus of the present invention;

FIG. 6A is a diagram showing a frame configuration example of a digitalwireless communication apparatus of the present invention;

FIG. 6B is a diagram showing a relationship between the amplitude andtime when a reception signal (I component) is received.

FIG. 6C is a diagram showing a relationship between the amplitude andtime when a reception signal (Q component) is received.

FIG. 7 is a diagram showing a signal space diagram example according toa 16APSK modulation type in the digital wireless communication apparatusof the present invention;

FIG. 8 is a diagram showing a frame configuration example according tothe 16APSK modulation type in the digital wireless communicationapparatus of the present invention;

FIG. 9 is a diagram showing a signal space diagram example according toa multivalue QAM system with 8 or more values in the digital wirelesscommunication apparatus of the present invention;

FIG. 10 is a diagram showing a frame configuration example according tothe multivalue QAM system with 8 or more values in the digital wirelesscommunication apparatus of the present invention;

FIG. 11 is a diagram showing a signal space diagram example according toa 64QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 12 is a diagram showing a frame configuration example according tothe 64QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 13 is a diagram showing another signal space diagram exampleaccording to the 64QAM system in the digital wireless communicationapparatus of the present invention;

FIG. 14 is a diagram showing a further signal space diagram exampleaccording to the 64QAM system in the digital wireless communicationapparatus of the present invention;

FIG. 15 is a diagram showing a signal space diagram example according toa 32QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 16 is a diagram showing a frame configuration example according tothe 32QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 17 is a diagram showing a signal space diagram example according toa 16QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 18 is a diagram showing a frame configuration example according tothe 16QAM system in the digital wireless communication apparatus of thepresent invention;

FIG. 19 is a diagram showing another signal space diagram exampleaccording to the 16QAM system in the digital wireless communicationapparatus of the present invention;

FIG. 20 is a diagram showing a further signal space diagram exampleaccording to the 16QAM system in the digital wireless communicationapparatus of the present invention;

FIG. 21 is a diagram showing a signal space diagram example of a signalpoint according to a QPSK modulation type, pilot symbol signal point andeach one symbol immediately before and after the pilot symbol;

FIG. 22 is a diagram showing a frame configuration example of QPSKmodulation symbols and pilot symbols;

FIG. 23 is a diagram showing a signal space diagram example of π/4-shiftDQPSK modulation type signal points, pilot symbol signal points and eachone symbol immediately before and after the pilot symbol;

FIG. 24 is a diagram showing a frame-configuration example of π/4-shiftDQPSK modulation symbols and pilot symbols.

FIG. 25 is a diagram showing a signal space diagram according to a 16QAMsystem in the digital wireless communication apparatus of the presentinvention; and

FIG. 26 is a diagram showing a relationship between the input power andoutput power of an amplifier in the digital wireless communicationapparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 2A and FIG. 2B, if a reception signal is detected attime 2 at which a time offset is generated, an error from signal point 3of a pilot symbol occurs, and therefore amplitude errors X_(I) and X_(Q)may occur. Because of this, the accuracy in estimating the phase,amplitude variation and frequency offset on the I-Q plane deteriorates.

At this time, the simplest pilot symbol configuration is to have 3consecutive pilot symbols as shown in FIG. 3. In such a configuration,even if a time offset occurs, the error from a pilot symbol signal pointreduces because there are 3 consecutive pilot symbols.

However, since no pilot symbols are transmitted immediately before andafter the pilot symbol to transmit information, this results in aproblem in terms of the transmission efficiency. Thus, the presentinvention suppresses deterioration of the information transmissionefficiency and suppresses errors from pilot symbol signal points when atime offset occurs by modulating symbols immediately before and after apilot symbol according to a modulation type different from the pilotsymbol modulation type. Thus, the present invention can suppressdeterioration of the error rate by suppressing deterioration of theaccuracy in estimating the phase, amplitude variation and frequencyoffset on the I-Q plane.

As the multivalue modulation type, the present specification includes a64QAM system, 32QAM system, 16QAM system, 8PSK modulation type, QPSKmodulation type, 16APSK modulation type and π/4-shift DQPSK modulationtype.

With reference now to the attached drawings, the embodiments of thepresent invention are explained in detail below.

Embodiment 1

FIG. 4 is a block diagram showing a configuration of the transmitterside of a digital wireless communication apparatus of the presentinvention. FIG. 5 is a block diagram showing a configuration of thereceiver side of a digital wireless communication apparatus of thepresent invention. FIG. 6A is a diagram showing a frame configurationused in the digital wireless communication apparatus of the presentinvention.

The following is an explanation of a case where the modulation type usedis a multivalue modulation type.

On the transmitter side shown in FIG. 4, transmission data are sent toquadrature baseband signal generating section (for multivalue modulationtype) 101 and quadrature baseband signal generating section (formodulation type for symbols immediately before and after PL) 102. Frametiming signal generating section 108 generates a frame timing signal attiming indicating a frame configuration shown in FIG. 6A and outputs theframe timing signal to quadrature baseband signal generating section(for multivalue modulation type) 101, quadrature baseband signalgenerating section (for modulation type for symbols immediately beforeand after PL) 102 and quadrature baseband signal generating section (forPL) 103.

Quadrature baseband signal generating section (for multivalue modulationtype) 101 receives transmission data and a frame timing signal as inputsand if the frame timing signal indicates a multivalue modulation symbol,quadrature baseband signal generating section (for multivalue modulationtype) 101 outputs the I component of the quadrature baseband signal forthe multivalue modulation type to I component switching section 104 andoutputs the Q component of the quadrature baseband signal for themultivalue modulation type to Q component switching section 105.

Quadrature baseband signal generating section (for modulation type forsymbols immediately before and after PL) 102 receives transmission dataand a frame timing signal as inputs and if the frame timing signalindicates a symbol immediately before or after the pilot symbol,quadrature baseband signal generating section (for modulation type forsymbols immediately before and after PL) 102 outputs the I component ofthe quadrature baseband signal for the modulation type for symbolsimmediately before and after PL to I component switching section 104 andoutputs the Q component of the quadrature baseband signal for themodulation type for symbols immediately before and after PL to Qcomponent switching section 105.

Quadrature baseband signal generating section (for PL) 103 receives aframe timing signal as an input and if the frame timing signal indicatesa pilot symbol, quadrature baseband signal generating section (for PL)103 outputs the I component of the pilot symbol quadrature basebandsignal to I component switching section 104 and outputs the Q componentof the pilot symbol quadrature baseband signal to Q component switchingsection 105.

I component switching section 104 receives the I component of thequadrature baseband signal for the multivalue modulation type, the Icomponent of quadrature baseband signal for symbols immediately beforeand after PL and the I component of the PL quadrature baseband signaland a frame timing signal as inputs, and switches between the Icomponent of the quadrature baseband signal for the multivaluemodulation type, the I component of quadrature baseband signal forsymbols immediately before and after PL and the I component of pilotsymbol quadrature baseband signal according to the frame timing signaland outputs them to a section for radio frequency (radio section) 106 asthe I component of the transmission quadrate baseband signal.

Q component switching section 105 receives the Q component of thequadrature baseband signal for the multivalue modulation type, the Qcomponent of quadrature baseband signal for symbols immediately beforeand after PL and the Q component of the PL quadrature baseband signaland a frame timing signal as inputs, and switches between the Qcomponent of the quadrature baseband signal for the multivaluemodulation type, the Q component of quadrature baseband signal forsymbols immediately before and after PL and the Q component of pilotsymbol quadrature baseband signal according to the frame timing signaland outputs them to radio section 106 as the Q component of thetransmission quadrate baseband signal.

Radio section 106 receives the I component and Q component of thetransmission quadrature baseband signal as inputs, carries outpredetermined radio processing on the baseband signal and then outputs atransmission signal. This transmission signal is amplified by poweramplifier 107 and the amplified transmission signal is output fromtransmission antenna 109.

On the receiver side shown in FIG. 5, radio section 202 receives thesignal received from antenna 201 as an input, quadrature-modulates theinput signal and outputs the I component and Q component of thereception quadrature baseband signal.

Frame timing signal generating section 205 receives the I component andQ component of the reception quadrature baseband signal as inputs,detects a frame configuration shown in FIG. 6A and outputs a frametiming signal to multivalue modulation type detection section 207,frequency offset amount estimating section 204 and modulation typedetection section (for symbols immediately before and after PL) 208.

Amplitude distortion amount estimating section 203 receives the Icomponent and Q component of the reception quadrature baseband signaland frame timing signal as inputs, extracts a pilot symbol, estimatesthe amount of amplitude distortion from the I component and Q componentof the pilot symbol quadrature baseband signal and outputs the amplitudedistortion amount estimation signal to multivalue modulation typedetection section 207 and modulation type detection section (for symbolsimmediately before and after PL) 208.

Frequency offset amount estimating section 204 receives the I componentand Q component of the reception quadrature baseband signal and frametiming signal as inputs, extracts a pilot symbol, estimates the amountof frequency offset from the I component and Q component of the pilotsymbol quadrature baseband signal and outputs the frequency offsetamount estimating signal to multivalue modulation type detection section207 and modulation type detection section (for symbols immediatelybefore and after PL) 208.

Multivalue modulation type detection section 207 receives the Icomponent and Q component of the reception quadrature baseband signal,frame timing signal, amplitude distortion amount estimating signal andfrequency offset estimating signal as inputs, carries out detection whenthe input is a multivalue modulation type symbol and outputs a receptiondigital signal according to the multivalue modulation type.

Modulation type detection section (for symbols immediately before andafter PL) 208 receives the I component and Q component of the receptionquadrature baseband signal, frame timing signal, amplitude distortionamount estimating signal and frequency offset estimating signal asinputs, carries out detection when the inputs are symbols immediatelybefore and after a pilot symbol and outputs a reception digital signalaccording to the modulation type of the symbols immediately before andafter the pilot symbol.

In the digital wireless communication apparatus in the configurationabove, a signal in a frame configuration as shown in FIG. 6A istransmitted/received. That is, the modulation type that modulates pilotsymbols is different from the modulation type that modulates symbol 301immediately before the pilot symbol and symbol 302 immediately after thepilot symbol. It is especially desirable that the number of multivaluesin the modulation type for modulating symbols immediately before andafter the pilot symbol be smaller than the number of multivalues in themodulation type for modulating pilot symbols.

For example, as shown in FIG. 6B and FIG. 6C, if the modulation type ofpilot symbol 305 is QPSK modulation and the modulation type of symbol306 immediately before and after the pilot symbol is 16QAM, when a timeoffset (jitter) from ideal judgment time 303 occurs (time 304), errors(amplitude errors) Y_(I) and Y_(Q) from the signal point occur becauseof the time offset. These errors (amplitude errors) Y_(I) and Y_(Q) aremuch smaller than amplitude errors X_(I) and X_(Q) shown in FIG. 2A andFIG. 2B.

Thus, because the modulation type for modulating pilot symbols isdifferent from the modulation type for modulating symbols immediatelybefore and after a pilot symbol, it is possible to suppress errors frompilot symbol signal points when a time offset occurs while suppressingdeterioration of the information transmission efficiency. As a result,it is possible to suppress deterioration of the accuracy in estimatingthe phase, amplitude variation and frequency offset on the I-Q plane andsuppress deterioration of the error rate.

In the present invention, the method for differentiating the modulationtype for modulating pilot symbols from the modulation type formodulating symbols immediately before and after a pilot symbol includes,for example, a method of placing two or more signal points of each onesymbol immediately before and after a pilot symbol on a virtual lineconnecting the pilot symbol signal point and the origin on the in-phaseI-quadrature Q plane. In this case, it is desirable to use a modulationtype with fewer multivalues than the pilot symbol modulation type with 8or more values for symbols immediately before and after the pilotsymbol.

The digital wireless communication apparatus of the present inventionhas both the configuration on the transmitter side shown in FIG. 4 andthe configuration on the receiver side shown in FIG. 5. Theconfigurations in FIG. 4 and FIG. 5 are only examples and the presentinvention is not limited to these examples only.

Embodiment 2

FIG. 7 shows a signal space diagram on the in-phase I-quadrature Q planeaccording to a 16APSK modulation type, which is an example of amultivalue modulation type with 8 or more values, indicating pilotsymbol signal points and signal points of one symbol before and afterthe pilot symbols. In FIG. 7, reference codes 401 indicate signal pointsaccording to the 16APSK modulation type, reference code 402 indicatesthe pilot symbol signal point and reference codes 403 indicate thesignal points of each one symbol immediately before and after the pilotsymbol. Furthermore, reference code 404 is a virtual line connecting thepilot symbol signal point and the origin on the I-Q plane, and two ormore signal points 403 of each one symbol immediately before and afterthe pilot symbol are placed on virtual line 404 connecting the pilotsymbol signal point 402 and the origin.

FIG. 8 shows a frame configuration example of symbols and pilot symbolsmodulated according to the 16APSK modulation type. Reference code 301indicates one symbol immediately before a pilot symbol and referencecode 302 indicates one symbol immediately after the pilot symbol. Atthis time, 2 or more signal points of one symbol 301 immediately beforethe pilot symbol and one symbol 302 immediately after the pilot symbolare placed on virtual line 404 connecting pilot symbol signal point 402and the origin on the in-phase I-quadrature Q plane.

If the transmission data is a digital signal modulated according to themodulation type shown in FIG. 7 and FIG. 8, even if symbolsynchronization is not completely established, the pilot symboltransitions on the virtual line connecting the pilot symbol and theorigin on the in-phase I-quadrature Q plane, and therefore the presentembodiment demonstrates the effects shown in FIG. 6B and FIG. 6C, makingit possible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This improves the bit error rate characteristic in the carrier to noiseratio during detection of a reception signal.

By the way, the locations of the pilot symbol signal point and signalpoints of each one symbol immediately before and after the pilot symbolon the in-phase I-quadrature Q plane are not limited to FIG. 7. Theframe configuration is not limited to FIG. 8, either. The presentembodiment explains the case where the multivalue modulation type with 8or more values is a 16APSK modulation type, but the multivaluemodulation type with 8 or more values is not limited to this.

As shown above, the digital wireless communication apparatus accordingto Embodiment 2 places signal points of each one symbol immediatelybefore and after the pilot symbol on a virtual line connecting theorigin and pilot symbol signal point on the in-phase-quadrature plane,in a frame configuration in which one pilot symbol is inserted for every3 symbols according to the modulation type including a multivaluemodulation type with 8 or more values, and in this way can suppressdeterioration of the accuracy in estimating the reference phase and theamount of frequency offset by the pilot symbol in quasi-coherentdetection of symbols whose symbol synchronization is not completelyestablished, improving the bit error rate characteristic in the signalto noise ratio.

Embodiment 3

FIG. 9 shows a signal space diagram according to a multivalue quadratureamplitude modulation (QAM) system with 8 or more values on the in-phaseI-quadrature Q plane and shows pilot symbol signal point and signalpoints of each one symbol immediately before and after the pilot symbol.In FIG. 9, reference codes 501 indicate the signal points according tothe multivalue QAM system, reference code 502 indicates a pilot symbolsignal point and reference codes 503 indicate signal points of each onesymbol immediately before and after the pilot symbol. Reference code 504is a virtual line connecting the pilot symbol signal point and theorigin on the I-Q plane. Two or more signal points 503 of each onesymbol immediately before and after the pilot symbol are placed onvirtual line 504 connecting pilot symbol signal point 502 and theorigin.

FIG. 10 shows a frame configuration example of symbols and pilot symbolsmodulated according to the multivalue QAM system with 8 or more values.Reference code 301 indicates one symbol immediately before the pilotsymbol and reference code 302 indicates one symbol immediately after thepilot symbol. At this time, two or more symbols 301 immediately beforethe pilot symbol and symbols 302 immediately after the pilot symbol areplaced on virtual line 504 connecting pilot symbol signal point 502 andthe origin on the in-phase I-quadrature Q plane.

When the digital signal modulated according to such a modulation type isdetected, even if symbol synchronization is not completely establishedas in the case of the embodiment above, the pilot symbol transitions onthe virtual line connecting the pilot symbol and the origin on thein-phase I-quadrature Q plane, and therefore the present embodimentdemonstrates the effects shown in FIG. 6B and FIG. 6C, making itpossible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This improves the bit error rate characteristic in the signal to noiseratio during detection of the reception signal.

The locations of pilot symbol signal point and signal points of each onesymbol immediately before and after the pilot symbol are not limited toFIG. 9. Moreover, the frame configuration is not limited to FIG. 10.

As shown above, the digital wireless communication apparatus accordingto Embodiment 3 places two or more signal points of each one symbolimmediately before and after the pilot symbol on a virtual lineconnecting the origin and pilot symbol signal point on thein-phase-quadrature plane, in a frame configuration in which one pilotsymbol is inserted for every 3 or more symbols according to themodulation type including the multivalue QAM systems with 8 or morevalues, and in this way can suppress deterioration of the accuracy inestimating the reference phase and the amount of frequency offset by thepilot symbol in quasi-coherent detection of symbols whose symbolsynchronization is not completely established, improving the bit errorrate characteristic in the signal to noise ratio.

Embodiment 4

FIG. 11 shows a signal space diagram according to a 16QAM system on thein-phase I-quadrature Q plane and shows a pilot symbol signal point andsignal points of each one symbol immediately before and after the pilotsymbol. In FIG. 11, reference codes 601 indicate signal points accordingto the 16QAM system, reference code 602 indicates the pilot symbolsignal point and reference codes 603 indicate signal points of each onesymbol immediately before and after the pilot symbol. Reference code 604is a virtual line connecting the pilot symbol signal point and theorigin on the I-Q plane. Two or more signal points 603 of each onesymbol immediately before and after the pilot symbol are placed onvirtual line 604 connecting pilot symbol signal point 602 and theorigin.

FIG. 12 shows a frame configuration example of symbols modulatedaccording to the 64QAM system and pilot symbols. Reference code 301indicates one symbol immediately before the pilot symbol and referencecode 302 indicates one symbol immediately after the pilot symbol. Atthis time, two or more signal points 603 of one symbol 301 immediatelybefore the pilot symbol and one symbol 302 immediately after the pilotsymbol are placed on virtual line 604 connecting signal point 602 of thepilot symbol and the origin on the in-phase I-quadrature Q plane.

When the digital signal modulated according to such a modulation type isdetected, even if symbol synchronization is not completely establishedas in the case of the embodiment above, the pilot symbol transitions onthe virtual line connecting the pilot symbol and the origin on thein-phase I-quadrature Q plane, and therefore the present embodimentdemonstrates the effects shown in FIG. 6B and FIG. 6C, making itpossible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This improves the bit error rate characteristic in the signal to noiseratio during detection of the reception signal.

The locations of the pilot symbol signal point and signal points of eachone symbol immediately before and after the pilot symbol on the in-phaseI-quadrature Q plane are not limited to FIG. 11. Moreover, the frameconfiguration is not limited to FIG. 12.

FIG. 13 shows another signal space diagram example according to the64QAM system on the in-phase I-quadrature Q plane and shows a pilotsymbol signal point and signal points of each one symbol immediatelybefore and after the pilot symbol. In FIG. 13, reference codes 701 and701-A indicate signal points according to the 64QAM system, referencecodes 701-A indicate signal points of each one symbol immediately beforeand after the pilot symbol, reference code 702 indicates a pilot symbolsignal point and reference code 703 indicates a virtual line connectingthe pilot symbol signal point and the origin on the I-Q plane.

If the signal point with the maximum signal point power of the64QAM-based signal points is designated as pilot symbol signal point 702and signal points 701-A on virtual line 703 connecting this and theorigin are designated as the signal points of symbol 301 immediatelybefore the pilot symbol and the signal point of one symbol 302immediately after the pilot symbol, the pilot symbol transitions on thevirtual line connecting the pilot symbol and the origin on the in-phaseI-quadrature Q plane even if symbol synchronization is not completelyestablished, and therefore it is possible to suppress deterioration ofthe accuracy in estimating the reference phase and the amount offrequency offset by the pilot symbol. This makes it possible to improvethe bit error rate characteristic in the signal to noise ratio duringdetection of the reception signal. Moreover, this case has an advantagethat it is possible to judge one symbol 301 immediately before the pilotsymbol and one symbol 302 immediately after the pilot symbol using a64QAM-based judgment method.

In FIG. 13, reference code 702 is used as the pilot symbol signal point,but the pilot symbol signal point is not limited to this and can be anysignal point if the signal point has the maximum signal point power ofthe 64QAM-based signal points.

FIG. 14 shows a further example of the 64QAM-based signal space diagramon the in-phase I-quadrature Q plane and shows a pilot symbol signalpoint and signal points of each one symbol immediately before and afterof the pilot symbol. In FIG. 14, reference codes 801 indicate64QAM-based signal points, reference code 802 indicates a pilot symbolsignal point, and reference codes 803 indicate signal points of each onesymbol immediately before and after the pilot symbol.

Signal points 801 are 64QAM-based signal points on the in-phaseI-quadrature Q plane, and if the maximum signal point power of the64QAM-based signal points is r² and the signal point power of the pilotsymbol is R², then the relationship between these two is R²=r². If thepoints of intersection of the virtual line or the I axis connectingpilot symbol signal point 802 placed on the I axis and the origin, andthe virtual line drawn from 64QAM-based signal point 801 perpendicularto the I axis are designated as signal points of symbol 301 immediatelybefore the pilot symbol and one symbol 302 immediately after the pilotsymbol, the pilot symbol transitions on the virtual line connecting thepilot symbol and the origin on the in-phase I-quadrature Q plane even ifsymbol synchronization is not completely established, and therefore thepresent embodiment demonstrates the effects shown in FIG. 6B and FIG.6C, making it possible to suppress deterioration of the accuracy inestimating the reference phase and the amount of frequency offset by thepilot symbol. This improves the bit error rate characteristic in thesignal to noise ratio during detection of the reception signal.

Furthermore, this configuration has an advantage that it is possible tojudge one symbol 301 immediately before the pilot symbol and one symbol302 immediately after the pilot symbol using a 64QAM-based judgmentmethod.

By the way, R²=r² is assumed in FIG. 14, but this limitation is notfixed. Moreover, a pilot symbol signal point to be placed on the I axiscan be any signal point other than signal point 802.

As shown above, the digital wireless communication apparatus accordingto Embodiment 4 places two or more signal points of each one symbolimmediately before and after the pilot symbol on a virtual lineconnecting the origin and pilot symbol signal point on thein-phase-quadrature plane, in the modulation type including the 64QAMsystem, and in this way can suppress deterioration of the accuracy inestimating the reference phase and the amount of frequency offset by thepilot symbol in quasi-coherent detection of symbols whose symbolsynchronization is not completely established, improving the bit errorrate characteristic in the signal to noise ratio.

Embodiment 5

FIG. 15 shows a signal space diagram according to a 32QAM system on thein-phase I-quadrature Q plane and shows a pilot symbol signal point andsignal points of each one symbol immediately before and after the pilotsymbol.

In FIG. 15, reference codes 901 indicate signal points according to the32QAM system, reference code 902 indicates a pilot symbol signal pointand reference codes 903 indicate signal points of every one symbolimmediately before and after the pilot symbol. Reference code 904 is avirtual line connecting the pilot symbol signal point and the origin onthe I-Q plane. Two or more signal points 903 of each one symbolimmediately before and after the pilot symbol are placed on virtual line904 connecting pilot symbol signal point 902 and the origin.

FIG. 16 shows a frame configuration example of 32QAM-based symbols andpilot symbols. Reference code 301 indicates one symbol immediatelybefore the pilot symbol and reference code 302 indicates one symbolimmediately after the pilot symbol.

At this time, as shown in FIG. 16, two or more signal points of onesymbol 301 immediately before the pilot symbol and one symbol 302immediately after the pilot symbol are placed on virtual line 904connecting pilot symbol signal point 902 and the origin on the in-phaseI-quadrature Q plane.

In Embodiment 5, as in the case of the embodiment above, even if symbolsynchronization is not completely established, the pilot symboltransitions on the virtual line connecting the pilot symbol and theorigin on the in-phase I-quadrature Q plane, and therefore the presentembodiment demonstrates the effects shown in FIG. 6B and FIG. 6C, makingit possible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This improves the bit error rate characteristic in the signal to noiseratio during detection of the reception signal.

The locations of the pilot symbol signal point and signal points of eachone symbol immediately before and after the pilot symbol on the in-phaseI-quadrature Q plane are not limited to FIG. 15. Moreover, the frameconfiguration is not limited to FIG. 16.

As shown above, the digital wireless communication apparatus accordingto Embodiment 5 places two or more signal points of each one symbolimmediately before and after the pilot symbol on a virtual lineconnecting the origin and pilot symbol signal point on thein-phase-quadrature plane, and in this way can suppress deterioration ofthe accuracy in estimating the reference phase and the amount offrequency offset by the pilot symbol in quasi-coherent detection ofsymbols whose symbol synchronization is not completely established,improving the bit error rate characteristic in the signal to noiseratio.

Embodiment 6

FIG. 17 is a 16QAM-based signal space diagram on the in-phaseI-quadrature Q plane and shows a pilot symbol signal point and signalpoints of each one symbol immediately before and after the pilot symbol.In FIG. 17, reference codes 1001 indicate 64QAM-based signal points,reference code 1002 indicates a pilot symbol signal point and referencecodes 1003 indicate signal points of each one symbol immediately beforeand after the pilot symbol. Reference code 1004 is a virtual lineconnecting the pilot symbol signal point and the origin on the I-Qplane. Two or more signal points 1003 of each one symbol immediatelybefore and after the pilot symbol are placed on virtual line 1004connecting pilot symbol signal point 1002 and the origin.

FIG. 18 shows a frame configuration example of 64QAM-based symbols andpilot symbol. Reference code 301 indicates one symbol immediately beforethe pilot symbol and reference code 302 indicates one symbol immediatelyafter the pilot symbol. At this time, two or more signal points of onesymbol 301 immediately before the pilot symbol and one symbol 302immediately after the pilot symbol are placed on virtual line 1004connecting pilot symbol signal point 1002 and the origin on the in-phaseI-quadrature Q plane.

In the digital wireless communication apparatus according to Embodiment6, as in the case of the embodiment above, even if symbolsynchronization is not completely established, the pilot symboltransitions on the virtual line connecting the pilot symbol and theorigin on the in-phase I-quadrature Q plane, and therefore it ispossible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This improves the bit error rate characteristic in the signal to noiseratio during detection of the reception signal.

The locations of the pilot symbol signal point and signal points of eachone symbol immediately before and after the pilot symbol on the in-phaseI and quadrature Q plane are not limited to FIG. 17. Moreover, the frameconfiguration is not limited to FIG. 18.

FIG. 19 shows another signal space diagram example of the 16QAM systemon the in-phase I-quadrature Q plane and shows a pilot symbol signalpoint and signal points of each one symbol immediately before and afterthe pilot symbol. In FIG. 19, reference codes 1101 and 1101-A indicate16QAM-based signal points, reference codes 1101-A indicate signal pointsof each one symbol immediately before and after the pilot symbol,reference code 1102 indicates the pilot symbol signal point andreference code 1103 indicates a virtual line connecting the pilot symbolsignal point and the origin.

If the signal point with the maximum signal point power of the16QAM-based signal points is designated as pilot symbol signal point1102 and signal points 1101-A on virtual line 1103 connecting this andthe origin are designated as the signal point of symbol 301 immediatelybefore the pilot symbol and one symbol 302 immediately after the pilotsymbol, the pilot symbol transitions on the virtual line connecting thepilot symbol and the origin on the in-phase I-quadrature Q plane even ifsymbol synchronization is not completely established, and therefore thepresent embodiment demonstrates the effects shown in FIG. 6B and FIG. 6Cand can suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbol.This makes it possible to improve the bit error rate characteristic inthe signal to noise ratio during detection of the reception signal.

Moreover, this configuration has an advantage that it is possible tojudge one symbol 301 immediately before the pilot symbol and one symbol302 immediately after the pilot symbol using a 16QAM-based judgmentmethod.

In FIG. 19, signal point 1102 is designated as the pilot symbol signalpoint, but the pilot symbol signal point is not limited to this and canbe any signal point if the signal point has the maximum signal pointpower of the 16QAM-based signal points.

FIG. 20 shows a further example of the 16QAM-based signal space diagramon the in-phase I-quadrature Q plane and shows a pilot symbol signalpoint and signal points of each one symbol immediately before and afterthe pilot symbol. In FIG. 20, reference codes 1201 indicate 16QAM-basedsignal points, reference code 1202 indicates a pilot symbol signalpoint, and reference codes 1203 indicate signal points of each onesymbol immediately before and after the pilot symbol.

In this case, if the maximum signal point power of the 16QAM-basedsignal points is p² and the pilot symbol signal point power is P²,suppose P²=p². If the points of intersection of the virtual line or theI axis connecting pilot symbol signal point 1202 placed on the I axisand the origin, and the virtual line drawn from 16QAM-based signal point1201 perpendicular to the I axis are designated as signal points ofsymbol 301 immediately before the pilot symbol and one symbol 302immediately after the pilot symbol, the pilot symbol transitions on thevirtual line connecting the pilot symbol and the origin on the in-phaseI-quadrature Q plane even if symbol synchronization is not completelyestablished, and therefore the present embodiment demonstrates theeffects shown in FIG. 6B and FIG. 6C, making it possible to suppressdeterioration of the accuracy in estimating the reference phase and theamount of frequency offset by the pilot symbol. This improves the biterror rate characteristic in the signal to noise ratio during detectionof the reception signal. Furthermore, this configuration has anadvantage that it is possible to judge one symbol 301 immediately beforethe pilot symbol one symbol 302 immediately after the pilot symbol usinga 16QAM-based judgment method.

By the way, P²=p² is assumed in FIG. 20, but this limitation is notfixed. Moreover, a pilot symbol signal point to be placed on the I axiscan be any signal point other than signal point 1202.

Embodiment 7

FIG. 21 is a signal space diagram according to a QPSK modulation type onthe in-phase I-quadrature Q plane and shows a pilot symbol signal pointand signal points of each one symbol immediately before and after thepilot symbol. In FIG. 21, reference codes 1301 and 1301-A indicatesignal points according to the QPSK modulation type, reference codes1301-A indicate signal points of each one symbol immediately before andafter the pilot symbol. Reference code 1302 is a virtual line connectingthe pilot symbol signal point and the origin.

FIG. 22 shows a frame configuration example of QPSK modulation symbolsand pilot symbols at time t. Reference code 301 indicates one symbolimmediately before the pilot symbol and reference code 302 indicates onesymbol immediately after the pilot symbol.

FIG. 21 shows the locations of signal points according to the QPSKmodulation type on the in-phase I-quadrature Q plane, pilot symbolsignal point and signal points 1301-A of each one symbol immediatelybefore and after the pilot symbol. Two signal points 1301-A of each onesymbol immediately before and after the pilot symbol are placed onvirtual line 1302 connecting pilot symbol signal point 1301-A and theorigin.

FIG. 22 shows a frame configuration example of QPSK modulation symbolsand pilot symbols at time t. Reference code 301 indicates one symbolimmediately before the pilot symbol and reference code 302 indicates onesymbol immediately after the pilot symbol.

At this time, two signal points of one symbol 301 immediately before thepilot symbol and one symbol 302 immediately after the pilot symbol areplaced on virtual line 1302 connecting pilot symbol signal point 1301-Aand the origin on the in-phase I-quadrature Q plane.

In this way, when estimating the reference phase and amount of frequencyoffset from the pilot symbol, even if symbol synchronization is notcompletely established, the pilot symbol transitions on the virtual lineconnecting the pilot symbol and the origin on the in-phase I-quadratureQ plane, and therefore the present embodiment demonstrates the effectsshown in FIG. 6B and FIG. 6C, making it possible to suppressdeterioration of the accuracy in estimating the reference phase and theamount of frequency offset by the pilot symbol. This improves the biterror rate characteristic in the signal to noise ratio during detectionof the reception signal.

The locations of pilot symbol signal point and signal points of each onesymbol immediately before and after the pilot symbol on the in-phase Iand quadrature Q plane are not limited to FIG. 21. Moreover, the frameconfiguration is not limited to FIG. 22.

As shown above, the digital wireless communication apparatus accordingto Embodiment 7 places two signal points of each one symbol immediatelybefore and after the pilot symbol on a virtual line connecting theorigin and pilot symbol signal point on the in-phase-quadrature plane,according to the modulation type including the QPSK modulation type inwhich one pilot symbol is inserted for every 3 or more symbols, and inthis way can suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbolin quasi-coherent detection of symbols whose symbol synchronization isnot completely established. This improves the bit error ratecharacteristic in the signal to noise ratio.

Embodiment 8

FIG. 23 is a signal space diagram according to a π/4-shift DQPSK(Differential Quadrature Phase Shift Keying) modulation type on thein-phase I-quadrature Q plane and shows a pilot symbol signal point andsignal points of each one symbol immediately before and after the pilotsymbol. In FIG. 23, reference codes 1401 and 1401-A indicate signalpoints according to a π/4-shift DQPSK modulation type, and especiallyreference codes 1401-A indicate signal points of each one symbolimmediately before and after the pilot symbol. Reference code 1402 is avirtual line connecting the pilot symbol signal point and the origin.

FIG. 24 shows a frame configuration example of π/4-shift DQPSKmodulation symbols and pilot symbols. Reference code 301 indicates onesymbol immediately before the pilot symbol and reference code 302indicates one symbol immediately after the pilot symbol.

FIG. 23 shows the locations of signal points 1401 and 1401-A accordingto the π/4-shift DQPSK modulation type on the in-phase I-quadrature Qplane, pilot symbol signal point 1401-A and signal points 1401-A of eachone symbol immediately before and after the pilot symbol. Two signalpoints 1401-A of each one symbol immediately before and after the pilotsymbol are placed on virtual line 1402 connecting pilot symbol signalpoint 1401-A and the origin.

FIG. 24 shows a frame configuration example of π/4-shift DQPSKmodulation symbols and pilot symbols. Reference code 301 indicates onesymbol immediately before the pilot symbol and reference code 302indicates one symbol immediately after the pilot symbol.

At this time, two signal points of one symbol 301 immediately before thepilot symbol and one symbol 302 immediately after the pilot symbol areplaced on virtual line 1402 connecting pilot symbol signal point 1401-Aand the origin on the in-phase I-quadrature Q plane.

In this way, when estimating the reference phase and the amount offrequency offset from the pilot symbol, even if symbol synchronizationis not completely established, the pilot symbol transitions on thevirtual line connecting the pilot symbol and the origin on the in-phaseI-quadrature Q plane, and therefore the present embodiment demonstratesthe effects shown in FIG. 6B and FIG. 6C, making it possible to suppressdeterioration of the accuracy in estimating the reference phase and theamount of frequency offset by the pilot symbol. This improves the biterror rate characteristic in the signal to noise ratio during detectionof the reception signal.

The locations of pilot symbol signal point and signal points of each onesymbol immediately before and after the pilot symbol on the in-phase Iand quadrature Q plane are not limited to FIG. 23. Moreover, the frameconfiguration is not limited to FIG. 24.

As shown above, the digital wireless communication apparatus accordingto Embodiment 8 places two signal points of each one symbol immediatelybefore and after the pilot symbol on a virtual line connecting theorigin and pilot symbol signal point on the in-phase-quadrature plane,according to the π/4-shift DQPSK modulation type in which one pilotsymbol is inserted for every 3 or more symbols, and in this way cansuppress deterioration of the accuracy in estimating the reference phaseand the amount of frequency offset by the pilot symbol in quasi-coherentdetection of symbols whose symbol synchronization is not completelyestablished. This improves the bit error rate characteristic in thesignal to noise ratio.

Embodiment 9

In a wireless communication apparatus, one of functions consuming alarge amount of power is a power amplifier. FIG. 25 shows a trail of theI component and Q component of a 16QAM quadrature baseband signal on theI-Q plane. At this time, suppose the in-phase signal is I and thequadrature signal is Q, then the available power amplifier is determinedby the maximum value of I²+Q², max (I²+Q²), and average value, ave(I²+Q²).

FIG. 26 is a diagram showing an input/output characteristic of the poweramplifier. In FIG. 26, reference code 1501 indicates a characteristiccurve of a power amplifier with large output power, reference code 1502indicates a characteristic curve of a power amplifier with small outputpower, reference code 1503 indicates average output power, referencecode 1504 indicates a modulation type with small variation of I²+Q² andreference code 1505 indicates a modulation type with large variation ofI²+Q².

At this time, when the average output power is indicated by referencecode 1503, amplification is possible using the power amplifier with thecharacteristic of reference code 1502 according to the modulation typeof reference code 1504, whereas amplification is not possible using thepower amplifier with the characteristic of reference code 1502 accordingto the modulation type of reference code 1505. Therefore, the poweramplifier with the characteristic of reference code 1501 should be used.

At this time, the power amplifier with the characteristic of referencecode 1501 has larger power consumption than the power amplifier with thecharacteristic of reference code 1502. In this way, the modulation typewith a smaller maximum value of I²+Q², max (I²+Q²), can use the poweramplifier with smaller power consumption. When focused on the locationof the pilot symbol signal point on the I-Q plane, the greater thedistance from the origin, the stronger noise resistance of the pilotsymbol the receiver side has, thus improving the bit error rate.

However, when focused on the power amplifier in the transmitter, it isnot desirable that the maximum value of I²+Q², max (I²+Q²), be increasedby increasing the pilot symbol.

Thus, the present embodiment increases the distance of the pilot symbolfrom the origin without increasing the maximum value of I²+Q², max(I²+Q²), on the I-Q plane. This makes it possible to improve the biterror rate in the receiver without increasing power consumption of thepower amplifier of the transmitter.

Then, the method of improving the bit error rate in the receiver withoutincreasing power consumption of the power amplifier of the transmitterin the present embodiment is explained taking as an example the casewhere a 16QAM system is used as the modulation type. In FIG. 25, themaximum value of I²+Q², max (I²+Q²), according to the 16QAM system comesto the position indicated by reference code 1601 on its way from signalpoint A to signal point A.

According to FIG. 17 and FIG. 18, from the relationship between thepilot symbol signal point, signal points 301 and 302 of each one symbolimmediately before and after the pilot symbol, even if the distance ofthe pilot symbol signal point from the origin on the I-Q plane isincreased more than the maximum amplitude at signal points in the 16QAMsystem as shown in FIG. 25, it is possible to keep that distance smallerthan the maximum value of I²+Q², max (I²+Q²), in the 16QAM system. Thismakes it possible to improve the bit error rate in the receiver withoutincreasing power consumption of the power amplifier of the transmitter,by increasing the amplitude at the pilot symbol signal point on the I-Qplane more than the maximum amplitude at signal points in the 16QAMsystem.

Suppose the amplitude at the pilot symbol signal point is greater thanthe maximum amplitude at multivalue modulation signal points on the I-Qplane. Furthermore, since the amplitude at the pilot signal symbol pointis increased, it is possible to improve the accuracy in estimating theamount of amplitude distortion and the amount of frequency offset on thereceiving side. As a result, it is possible to improve the bit errorrate characteristic.

Then, the effects of the present embodiment are explained in detail withreference to FIG. 9 and FIG. 10.

As shown in FIG. 9, the multivalue QAM signal space diagram on thein-phase I-quadrature Q plane is given in Equation 1 below:I _(QAM) =r(2^(m−1) a ₁+2^(m−2) a ₂+ . . . +2⁰ a _(m))Q _(QAM) =r(2^(m−1) b ₁+2^(m−2) b ₂+ . . . +2⁰ b _(m))  (1)where suppose signal points according to the multivalue QAM system areexpressed as (IQAM, QQAM), m is an integer, (a1, b1), (a2, b2), . . . ,(am, bm) are binary codes of 1, −1, and r is a constant.

Two or more signal points 503 of each one symbol immediately before andafter the pilot symbol are placed on virtual line 504 connecting pilotsymbol signal point 502 and the origin. As shown in FIG. 10, two or moresignal points of one symbol 301 immediately before the pilot symbol andone symbol 302 immediately after the pilot symbol on virtual line 504connecting pilot symbol signal point 502 and the origin on the in-phaseI-quadrature Q plane. In this way, even if symbol synchronization is notcompletely established, the pilot symbol transitions on a straight lineconnecting the pilot symbol and the origin on the in-phase I-quadratureQ plane, and therefore it is possible to suppress deterioration of theaccuracy in estimating the reference phase and the amount of frequencyoffset by the pilot symbol. This improves the bit error ratecharacteristic in the signal to noise ratio during detection of thereception signal.

Furthermore, if a maximum value of the multivalue QAM signal point poweron the in-phase I-quadrature Q plane is a and the pilot symbol signalpoint power on the in-phase I-quadrature Q plane is b, maintaining b>amakes it possible to improve the accuracy in estimating amplitudedistortion by the amplitude distortion estimating section and theaccuracy in estimating the amount of frequency offset by the frequencyoffset amount estimating section on the receiving side withoutdeteriorating the power efficiency of the power amplifier on thetransmitting side as described above. This improves the bit error ratecharacteristic in the signal to noise ratio during detection of thereception signal.

By the way, the locations of the pilot symbol signal point and signalpoints of each one symbol immediately before and after the pilot symbolon the in-phase I-quadrature Q plane are not limited to FIG. 9, butgreater effects are obtained especially when the pilot symbol signalpoint is placed on the axis. The frame configuration is not limited toFIG. 10.

Furthermore, if the frequency character of the route roll-off filter,which is a band limiting filter, is as shown in Equation 2 below,changing the roll-off factor from 0.1 to 0.4 and setting the signalpoint amplitude of the pilot symbol to a value greater than 1.0 time andsmaller than 1.6 times the maximum signal point amplitude according tothe multivalue QAM system can improve the accuracy in estimating theamount of frequency offset and the amount of amplitude distortion whencarrying out quasi-coherent detection. This results in a greater effectof improving the bit error rate characteristic in the signal to noiseratio. In Equation 2, ω is frequency in radian, α is roll-off factor, ω0 is Nyquist frequency in radian and H(ω) is amplitude characteristic ofthe route roll-off filter.

$\begin{matrix}{{H(\omega)} = \left\{ \begin{matrix}1 & {\omega \leqq {\omega_{0}\left( {1 - \alpha} \right)}} \\\sqrt{\frac{1}{2}\left\lbrack {1 - {\sin\left\{ {\frac{\pi}{2{\alpha\omega}_{0}}\left( {\omega - \omega_{0}} \right)} \right\}}} \right\rbrack} & {{\omega_{0}\left( {1 - \alpha} \right)} \leqq \omega \leqq {\omega_{0}\left( {1 + \alpha} \right)}} \\0 & {\omega \geqq {\omega_{0}\left( {1 + \alpha} \right)}}\end{matrix} \right.} & (2)\end{matrix}$

The present embodiment explains the multivalue QAM system as an exampleof a multivalue modulation type with 8 or more values, but themultivalue modulation type with 8 or more values is not limited to this.Moreover, a 64QAM system, 32QAM system, 16QAM system, 8PSK modulationtype and QPSK modulation type can also produce effects similar to thoseof the multivalue QAM system.

As shown above, the digital wireless communication apparatus accordingto Embodiment 9 places two or more signal points of each one symbolimmediately before and after the pilot symbol on a virtual lineconnecting the origin and pilot symbol signal point on thein-phase-quadrature plane, in the multivalue modulation type with 8 ormore values in which one pilot symbol is inserted for every 3 or moresymbols and increases the amplitude at the pilot symbol signal pointmore than the maximum amplitude at signal points according to themultivalue modulation type with 8 or more values. In this way, it ispossible to suppress deterioration of the accuracy in estimating thereference phase and the amount of frequency offset by the pilot symbolin quasi-coherent detection of symbols whose symbol synchronization isnot completely established, improve the bit error rate characteristic inthe signal to noise ratio and further improve the bit error ratecharacteristic in the signal to noise ratio without deteriorating thepower efficiency of the power amplifier on the transmitting side.

As shown above, the present invention differentiates the modulation typeimmediately before and after the pilot symbol from the modulation typeof the pilot symbol, and therefore can suppress deterioration of theaccuracy in estimating the reference phase and the amount of frequencyoffset by the pilot symbol in quasi-coherent detection of symbols whosesymbol synchronization is not completely established, improve the biterror rate characteristic in the signal to noise ratio. The presentinvention can further improve the bit error rate characteristic in thesignal to noise ratio without deteriorating the power efficiency of thepower amplifier on the transmitting side, by increasing the amplitude atthe pilot symbol signal point more than the maximum amplitude at signalpoints according to the multivalue modulation type.

The present invention is not limited to Embodiments 1 to 9, but can alsobe implemented with various modifications. Moreover, Embodiments 1 to 9can be implemented in a variety of combinations thereof as appropriate.

The present invention is not limited to the above described embodiments,and various variations and modifications may be possible withoutdeparting from the scope of the present invention.

This application is based on the Japanese Patent Application No. HEI11-010146 filed on Jan. 19, 1999 and the Japanese Patent Application No.HEI 11-213264 filed on Jul. 28, 1999, entire content of which isexpressly incorporated by reference herein.

1. A digital wireless communication method comprising: mapping a pilotsymbol on a one of first signal points in a signal space diagram,utilizing a pilot symbol mapping section; mapping a specific symbol on aone of second signal points in a signal space diagram, utilizing aspecific symbol mapping section, the second signal point of the mappedspecific symbol being different from the first signal point, one of anin-phase and quadrature components of the specific symbols being zero;mapping a data symbol on a one of third signal points in a signal spacediagram, the third signal points being different from the first signalpoint of the mapped pilot symbol and the second signal point of themapped specific symbol, utilizing a data symbol mapping section; andinserting the specific symbol immediately before or after the pilotsymbol, utilizing an inserting section.
 2. The digital wirelesscommunication method according to claim 1, wherein the third signalpoints are signal points selected from a 64QAM modulation scheme, a16QAM modulation scheme, and a QPSK modulation scheme.
 3. The digitalwireless communication method according to claim 1, wherein the signalpoint of the mapped pilot symbol has an amplitude greater than themaximum amplitude of the third signal points of the mapped data symbolin a signal space diagram.
 4. A digital wireless communication apparatuscomprising: a pilot symbol mapping section that maps a pilot symbol on aone of first signal points in a signal space diagram; a specific symbolmapping section that maps a specific symbol on a one of second signalpoints in a signal space diagram, the second signal point of the mappedspecific symbol being different from the first signal point, one ofin-phase and quadrature components of the specific symbols being zero; adata symbol mapping section that maps a data symbol on a one of thirdsignal points in a signal space diagram, the third signal point of themapped specific symbol being different from the first signal point ofthe mapped pilot symbol and the second signal point of the mappedspecific symbol; and an inserting section that inserts the specificsymbol immediately before or after the pilot symbol.
 5. The digitalwireless communication apparatus according to claim 4, wherein the thirdsignal points are signal points selected from a 64QAM modulation scheme,a 16QAM modulation scheme, and a QPSK modulation scheme.
 6. The digitalwireless communication apparatus according to claim 4, wherein thesignal point of the mapped pilot symbol has an amplitude greater thanthe maximum amplitude of signal points of mapped data symbol in a signalspace diagram.